Microencapsulation of materials using cenospheres

ABSTRACT

Disclosed are methods for incorporating core materials such as phase change materials or admixtures into building materials like concrete. The methods use cenospheres, which are then etched and loaded with the core material. The composition can also be coated with a thin film. Compositions containing cenospheres loaded with the various core materials are disclosed, as are building materials containing such compositions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/223,292 filed Jul. 29, 2016, which claims the benefit of priority toU.S. Provisional Application No. 62/198,997, filed Jul. 30, 2015, whichare hereby incorporated herein by reference in their entireties.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Grant No. 23006awarded by the National Science Foundation. The government has certainrights in the invention.

BACKGROUND

The buildings sector of the United States accounts for approximately 40%of the U.S. primary energy consumption and 39% of the U.S. carbondioxide emissions. To cope with this challenging situation, efforts areneeded to improve energy efficiency of U.S. buildings, which will notonly save money for both homeowners and business owners, but also reducethe environmental impacts of energy use.

One approach to address these issues has been to incorporate phasechange materials (PCMs) into construction materials to enhance thebuilding's energy efficiency through Thermal Energy Storage (TES) andthermal regulation. PCMs change their phase from solid to liquid andvice versa at their phase change temperatures with large amount ofenergy absorbed or released. Thermal inertia (mass) of the building canbe significantly increased by integrating PCMs into constructionmaterials. PCMs have been considered as a promising method of TES interms of narrowing the gap between the peak and off-peak loads ofenergy/electricity demand, reducing diurnal temperature fluctuations,and utilizing the free cooling at night for day peak cooling loadshaving.

Two primary methods have been used to incorporate PCMs into constructionmaterials: (1) microencapsulation of PCMs and (2) form-stable PCMscomposites. In the first method, PCMs are encapsulated within aprotective polymer shell. The produced microencapsulated PCMs canpreserve PCMs as long as possible through the heating/cooling cycles.This microencapsulation method increases the heat transfer area,decreases the reactivity of the PCMs, limits the interaction with theconstruction materials, enhances the low heat conductivity, andfacilitates the handling of the PCMs. However, it also suffers a fewdrawbacks preventing practical applications of the PCMs in constructionmaterials. For example, the protection shell is made of polymers thatusually have low mechanical stiffness and strength. As a result, themechanical stiffness and strength of the construction materials can bereduced significantly by adding the microcapsules. The microcapsules canalso been easily broken during the mixing of concrete, leading toleaking of the PCMs. The polymeric shell also has low chemical andthermal stability. It can be deteriorated by UV light, oxidation, andother aggressive chemicals. It can also lose its stability whentemperature exceeds its glass transition temperature. The polymer shellscan also be flammable, and therefore cannot be adopted by the buildingindustry. Further, the thermal conductivity of the polymer shells isoften very low, making thermal exchange between the PCMs inside theshell and the outside environment much more difficult.

In the second method, PCMs are first absorbed into porous materials suchas light weight aggregates and diatomite particles to form stablecomposites, which are then added into the construction materials. Whenusing porous particles to absorb PCM there are no protective layers onthe surface of the composites. As a result, PCMs can still leak from theporous material once the temperature exceeds the phase change materials,leading to reduction or loss of the claimed thermal storage capacity.

Similar approaches have been tried when introducing materials other thanPCMs into construction materials. This is especially prevalent whenintroducing admixtures into concrete. Incompatibility between theadmixtures and hydration of cement is a major problem in the manufactureof concrete when the admixture is directly added into the mix. Forexample, water reducers, the most commonly used admixtures in concretecan have undesirable side effects such as rapid loss of workability,excessive quickening/retardation of setting, reduced rates of strengthgain, and changes in long term behavior. Similarly, shrinkage reducingadmixtures, which are used to reduce drying and autogenous shrinkage inconcrete elements, can also cause side effects in concrete as theyreduce the rate of cement hydration and strength development inconcrete.

As a major ingredient of concrete, water is also used as an admixture inhigh strength concrete (HSC) to reduce autogenous shrinkage of theconcrete through internal curing. Autogenous shrinkage is mainly causedby the capillary tension in the pore fluid caused by self-shrinkage. Inthe case of HSC with a water to cement ratio (W/C) below 0.3, theautogenous shrinkage can account for more than 50% of the totalcontraction deformation. Serious cracking can be induced in early-ageconcrete by autogenous shrinkage. These cracking problems cannot bemitigated through conventional full water curing because of HSC'scompact pore structure and very low permeability. To minimize oreliminate autogenous shrinkage, additional moisture has to be providedwithin the concrete when it is needed. This additional moisture isessentially used as an admixture in concrete. However, it cannot beadded directly into concrete during mixing because the compressivestrength of HSC can be significantly reduced.

Undesirable interaction with cement hydration can prevent applicationsof some other admixtures in concrete. For example, bioactive agents havebeen shown to prevent corrosion of stainless steel and aluminum. Theyprovide an eco-friendly method to prevent the corrosion in concrete.However, when these bioactive agents are simply mixed in with concrete,the 28-day compressive strength of the concrete was reduced by more than60%. This is because the bioactive agents can cover the surface ofcement particles and therefore prevent the cement particle from reactingwith water, resulting in less CSH produced and much lower compressivestrength.

As with PCMs, polymer based microcapsules or porous composites have beentried as a way incorporate admixtures into concrete without impartingundesirable effects caused by interactions with the admixture andconcrete. For example, compositions that modify viscosity, impartantimicrobial properties, improve corrosion or fire resistance, ormodify the water needed have been microencapsulated or adsorbed intoporous composites and then mixed with concrete. As noted, however, thesemethods can have drawbacks such as breakage of the microcapsule, highmanufacturing cost, leakage of the admixture, poor delivery of theadmixture, or simply poor performance.

What are thus needed are new compositions and methods that can be usedto incorporate PCMs and other admixtures into building materials such asconcrete. The compositions and methods disclosed herein seek to addressthese and other needs.

SUMMARY

In accordance with the purposes of the disclosed materials, compounds,compositions, articles, devices, and methods, as embodied and broadlydescribed herein, the disclosed subject matter, in one aspect, relatesto compositions and methods for preparing and using the disclosedcompositions. In a further aspect, disclosed herein are compositionscomprising cenospheres and core materials, wherein the core material isencapsulated inside the cenosphere. In specific examples, the corematerial is a phase change material. This in a specific aspect,disclosed herein are compositions comprising cenospheres and PCMs,wherein the PCMs are encapsulated within the cenospheres. In furtherexamples, the core material is an admixture, such as viscositymodifiers, antimicrobial agents, corrosion inhibitors, fire retardants,water, air, and the like. Thus in a further aspect, disclosed arecompositions comprising cenospheres and any of such admixtures, wherethe admixtures are encapsulated inside the cenosphere. Methods of usingcenospheres to encapsulate core materials like PCMs and other admixturesare also disclosed. Also, methods of adding the disclosed compositionsto building materials such as concrete, and the materials producedthereby, are disclosed.

Additional advantages of the disclosed subject matter will be set forthin part in the description that follows, and in part will be obviousfrom the description, or can be learned by practice of the aspectsdescribed below. The advantages described below will be realized andattained by means of the elements and combinations particularly pointedout in the appended claims. It is to be understood that both theforegoing general description and the following detailed description areexemplary and explanatory only and are not restrictive.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, which are incorporated in and constitute apart of this specification, illustrate several aspects of the disclosureand together with the description, serve to explain the principles ofthe disclosure.

FIG. 1 is a schematic illustrating the general steps for preparing thedisclosed CenoPCMs.

FIGS. 2A through 2C are SEM images showing perforated cenosphereproduced by acid etching. FIG. 2A is an image of the impermeable shellbefore etching. FIG. 2B is an image of the porous shell of thecenosphere. FIG. 2C is an image of the perforated shell after etchingwith 1.0 M NH₄F-1.2 M HCl—H₂O for 2 hours.

FIGS. 3A and 3B are schematics illustrating the general steps forloading liquid PCM into perforated cenospheres. FIG. 3A shows thatbefore loading, cenospheres float on the liquid PCM. FIG. 3B shows thatafter the cenospheres are filled with the PCM, they settle down at thebottom of the container.

FIG. 4 is a schematic illustrating a spray-drying method to a seal theperforated cenospheres with sodium silicate.

FIGS. 5A through 5D are SEM images that compare cenoPCMs withcommercially available microencapsulated PCMs. FIG. 5A is an image ofMicronale, a product of BASF.

FIG. 5B is an image of a commercially available microencapsulated PCMproduced by CIBA, UK. FIG. 5C is an image of CenoPCM. FIG. 5D is animage of cenoPCM used in concrete.

FIGS. 6A and 6B are graphs from experiments characterizing CenoPCM. FIG.6A is a DSC measurement of CenoPCM. FIG. 6B is a graph of TGA results ofunsealed CenoPCM.

FIG. 7 is a graph of payback periods for the PCM-enhanced R-30 celluloseinsulation configuration installed on the attic floor as a function ofthe PCM price for a single-story ranch house in Bakersfield, Calif. Theexternal temperature profiles have been defined as “a”.

FIG. 8 is a schematic of the formation of nanosilica coating on acenosphere through sol-gel process.

FIGS. 9A and 9B are graphs showing the coated CenoPCM. FIG. 9A is aCenoPCM coated with a thin layer of nano-silica. FIG. 9B shows CenoPCMscoated with a polymer.

FIG. 10 is a graph of water released from perforated cenospheres.

FIGS. 11A through 11C are SEM images of concrete with water to cementratio=0.34 with and without cenospheres as internal curing agent. FIG.11A is a concrete without internal curing with significant amount ofdrying shrinkage cracks. FIG. 11B is a concrete with cenospheres asinternal curing agent showing cenospheres are evenly dispersed inconcrete and much less drying shrinkage cracks. FIG. 11C is a brokencenosphere in concrete showing water is released and very densehydration products around it.

DETAILED DESCRIPTION

The materials, compounds, compositions, articles, and methods describedherein may be understood more readily by reference to the followingdetailed description of specific aspects of the disclosed subject matterand the Examples and Figures included therein.

Before the present materials, compounds, compositions, and methods aredisclosed and described, it is to be understood that the aspectsdescribed below are not limited to specific synthetic methods orspecific reagents, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular aspects only and is not intended to be limiting.

Also, throughout this specification, various publications arereferenced. The disclosures of these publications in their entiretiesare hereby incorporated by reference into this application in order tomore fully describe the state of the art to which the disclosed matterpertains. The references disclosed are also individually andspecifically incorporated by reference herein for the material containedin them that is discussed in the sentence in which the reference isrelied upon.

General Definitions

In this specification and in the claims that follow, reference will bemade to a number of terms, which shall be defined to have the followingmeanings:

Throughout the description and claims of this specification the word“comprise” and other forms of the word, such as “comprising” and“comprises,” means including but not limited to, and is not intended toexclude, for example, other additives, components, integers, or steps.

As used in the description and the appended claims, the singular forms“a,” “an,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a composition”includes mixtures of two or more such compositions, reference to “thecompound” includes mixtures of two or more such compounds, reference to“an agent” includes mixture of two or more such agents, and the like.

“Optional” or “optionally” means that the subsequently described eventor circumstance can or cannot occur, and that the description includesinstances where the event or circumstance occurs and instances where itdoes not.

A weight percent (wt. %) of a component, unless specifically stated tothe contrary, is based on the total weight of the formulation orcomposition in which the component is included.

Reference will now be made in detail to specific aspects of thedisclosed materials, compounds, compositions, articles, and methods,examples of which are illustrated in the accompanying Examples andFigures.

Compositions

Disclosed herein are compositions that comprise a core materialencapsulated within cenospheres.

Cenospheres are hollow inorganic particles generated in coal burningpower plants with size ranging from a few micrometers to hundreds ofmicrometers, as shown in FIG. 2A. Cenospheres typically make up around1-2% of the fly ash and can be recovered or “harvested” from the flyash. These cenospheres derived from coal combustion are commerciallyavailable. A cenosphere is thus an industrial waste material and theiruse in the disclosed compositions provides a unique advantage in thatthey are being reused in a beneficial way, rather than being discarded.A cenosphere has an aluminosilicate shell with high stiffness andstrength and a thickness in a few micrometers. The shell has a porousstructure formed by gas inclusion and is covered by a glass-crystallinenanosize film, as shown in FIG. 2B. Cenospheres have been used inconstruction materials for decades to produce lightweight materials.These cenospheres were hollow and no method had been available toincorporate a material into the cenospheres was available. This isbecause the shell of the cenosphere is covered by a glass-crystallinenanosize film, as shown in FIG. 2A, making the inner volume of thecenosphere inaccessible. The disclosed methods have overcome thisbarrier and incorporate core material into the inner volume of thecenosphere.

In the disclosed compositions, the cenosphere can have an averagediameter of from about 1 μm to about 2,000 μm, from about 20 μm to about1,000 μm, or from about 30 μm to about 80 μm. In further examples, theaverage diameter of the cenosphere can be about 1, 10, 20, 30, 40, 50,60, 70, 80, 90, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200,1300, 1400, 1500, 1600, 1700, 1800, 1900, or 2000 μm, where any of thestated values can form an upper or lower endpoint when appropriate.

The payloads of the core material inside the cenospheres can be fromabout 20% to about 90%, about 50% to about 70% by weight, or about 60%by weight of the composition (core material plus cenosphere). In otherexamples, the disclosed compositions can contain about 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or 90% core material by weightof the composition, where any of the stated values can form an upper orlower endpoint when appropriate.

The disclosed compositions can also comprise a majority of intact,loaded, cenospheres. That is, before preparing the disclosedcompositions the cenosphere based starting material can be filtered toremove the broken cenospheres. This can be done via water filling undervacuum followed by gravity separation. Thus, intact cenospheres areisolated and used. In certain examples, this means the final cenospherecomposition, after loading, can comprise at least about 50, 60, 70, 80,or 90% by weight intact cenospheres.

The disclosed compositions can also comprise an outer coating on thecenosphere. Suitable outer coatings include silica, alumina, or titania.

PCMs

In one aspect, the disclosed compositions comprise a PCM as the corematerial that is inside a cenosphere. These are denoted herein as“CenoPCMs.”

A PCM is a composition with high latent heat that undergoes a phasechange at a desired temperature. For example, when a PCM freezes,changing from liquid to solid, it releases large amounts of energy inthe form of latent heat of fusion. When the material melts, an equalamount of energy is absorbed from the environment as it changes fromsolid to liquid. Likewise, when a PCM condenses from gas to liquid itreleases large amounts of energy in the form of latent heat ofvaporization, absorbing an equal amount of energy from the environmentas it boils, changing from liquid to gas.

In specific examples, a suitable PCM for the disclosed CenoPCMs cancomprise water, a salt-water solution, a sugar alcohol, a paraffin, afatty acid, a salt hydrate, a nitrate, a hydroxide, a hygroscopicmaterial, or combinations thereof. More specifically, the PCM can beurea; ureidopyrimidone; N,N-dialkylpiperidinum;N,N-dialkylpyrrolidinium; LiF and BeF₂; NaF and BeF₂; LiF and NaF andKF; NaF and ZrF₄; KNO₃ and KCl; KNO₃ and K₂CO₃; LiBr and KBr; KNO₃ andKBr; KNO₃ and LiOH; FeCl₂ and KCl; KCl and LiCl; K₂CO₃ and KOH; K₂SO₄and KOH; FeCl₂ and NaCl; KCl and MnCl₂; LiBr and LiI; KCl—MgCl₂; MnCl₂and NaCl; LiCO₃ and LiOH; LiBr and LiF; NaCl and MgCl₂; K₂CO₃ and MgCO₃;KF and KBF₄; Na₂SO₄ and ZnSO₄; CaCl₂ and LiCl; LiCl and Li₂SO₄; KF andLiF; K₂CO₃ and Li₂CO₃; Li₂CO₃ and Na₂CO₃; LiCl and LiF; CaCl₂ and NaCl;KVO₃ and BaTiO₃; KCl and LiBr and NaBr; KBr and LiCl and NaCl; LiBr andNaBr and KBr; NaOH and NaCl and Na₂CO₃; KCl and LiCl and Li₂SO₄; MgCl₂and KCl and NaCl; NaCl and KCl and FeCl₂; KCl and LiCl and CaF₂; CaCl₂and KCl and LiCl; NaCl and KCl and LiCl; KF and AlF₃ and ZrF₄; MnCl₂ andKCl and NaCl; Na₂SO₄ and K₂SO₄ and ZnSO₄; Na₂CO₃ and K₂CO₃ and ZnSO₄;Na₂CO₃ and K₂CO₃ and LiCO₃; KCl and NaCl and LiF; LiCl and NaCl andLi₂SO₄; LiCl and KCl and CaCl₂ and CaF₂; KCl and NaCl and LiCl andLi₂SO₄; NaNO₃; KNO₃; KNO₃ and KCl; KNO₃ and K₂CO₃; KNO₃ and KBr; FeCl₂and KCl; KCl and LiCl; K₂CO₃ and KOH; K₂SO₄ and KOH; FeCl₂ and NaCl;LiBr and KBr; NaOH and NaCl and Na₂CO₃; MgCl₂ and KCl and NaCl; NaCl andKCl and FeCl₂; CaCl₂ and KCl and LiCl; MgCl₂ and KCl and NaCl; MgCl₂ andKCl and NaCl; NaOH and NaCl and Na₂CO₃; MnCl₂ and KCl and NaCl; Na₂CO₂and K₂CO₃ and Li₂CO₃; LiF and LiCl and LiVO₃ and Li₂SO₄ and Li₂MoO₄; LiFand LiCl and Li₂SO₄ and Li₂MoO₄; LiF and KF and KCO₄ and KCl; LiF andLiOH; LiF and BaF₂ and KF and NaF; LiF and KF and NaF and KCl; LiF andNaF and KF and MgF₂; LiF and NaF and KF; LiF and KF and NaF; LiF and NaFand KF; LiF and LiCl; KF and LiCl; KF and LiCl; LiF and KF; LiF andLiVO₃ and Li₂MoO₄; LiCl and KCl and LiCO₃ and LiF; LiCl and KCl; KCl andMnCl₂ and NaCl; LiClLiVO₃ and Li₂MoO₄ and Li₂SO₄ and LiF; NaCl and KCland MgCl₂; KCl and MgCl₂ and NaCl; NaCl and MgCl₂; KCl and ZnCl₂; KCland MgCl₂; NaCl═MgCl₂; LiCl and Li₂SO₄ and Li₂MoO₄; KCl and MnCl₂; LiCland Li₂SO₄ and LiVO₃; KCl and MnCl₂; NaCl and MgCl₂; CaCl₂ and KCl andNaCl and NaF; CaCl₂ and KCl and MgCl₂ and NaCl; CaCl₂ and KCl and NaCl;KCl and MgCl₂; LiCl and LiF and MgF₂; CaCl₂ and CaF₂ and NaF; CaCl₂ andNaCl; NaOH and NaCl and Na₂CO₃; LiOH and LiF; Li₂CO₃ and K₂CO₃ andNa₂CO₃; Li₂CO₃ and K₂CO₃; Li₂CO₃ and K₂CO₃; Zn and Mg; Al and Mg and Zn;Mg and Cu and Zn; Mg and Cu and Ca; Mg and Al; formic acid; caprilicacid; glycerin; D-Lactic acid; methyl palmitate; camphenilone; docasylbromide; caprylone; phenol; heptadecanone; 1-cyclohexylooctadecane;4-heptadacanone; p-joluidine; cyanamide; methyl eicosanate;3-heptadecanone; 2-heptadecanone; hydrocinnamic acid; cetyl alcohol;α-nepthylamine; camphene; O-nitroaniline; 9-heptadecanone; thymol;sodium acetate; trimethylolethane; methylbehenate; diphenyl amine;p-dichlorobenzene; oxalate; hypophosphoric acid; O-xylene dichloride;β-chloroacetic acid; nitro naphthalene; trimyristin; heptaudecanoicacid; α-chloroacetic acid; bee wax; bees wax; glycolic acid; glyolicacid; p-bromophenol; azobenzene; acrylic acid; dinto toluent;phenylacetic acid; thiosinamine; bromcamphor; durene; benzylamine;methyl bromobenzoate; alpha napthol; glautaric acid; p-xylenedichloride; catechol; quinine; acetanilide; succinic anhydride; benzoicacid; stibene; benzamide; acetic acid; polyethylene glycol; capric acid;eladic acid; lauric acid; pentadecanoic acid; trustearin; myristic acid;palmatic acid; stearic acid; acetamide; methyl fumarate; K₂HPO₄.6H₂O;FeBr₃.6H₂O; Mn(NO₃)₂.6H₂O; FeBr₃.6H₂O; CaCl₂.12H₂O; LiNO₃.2H₂O;LiNO₃.3H₂O; Na₂CO₃.10H₂O; Na₂SO₄.10H₂O; KFe(SO₄)₂.12H₂O; CaBr₂.6H₂O;LiBr₂.2H₂O; Zn(NO₃)₂.6H₂O; FeCl₃.6H₂O; Mn(NO₃)₂.4H₂O; Na₂HPO₄.12H₂O;CoSO₄.7H₂O; KF.2H₂O; MgI₂.8H₂O; CaI₂.6H₂O; K₂HPO₄.7H₂O; Zn(NO₃)₂.4H₂O;Mg(NO₃).4H₂O; Ca(NO₃).4H₂O; Fe(NO₃)₃.9H₂O; Na₂SiO₃.4H₂O; K₂HPO₄.3H₂O;Na₂S₂O₃.5H₂O; MgSO₄.7H₂O; Ca(NO₃)₂.3H₂O; Zn(NO₃)₂.2H₂O; FeCl₃.2H₂O;Ni(NO₃)₂.6H₂O; MnCl₂.4H₂O; MgCl₂.4H₂O; CH₃COONa.3H₂O; Fe(NO₃)₂.6H₂O;NaAl(SO₄)₂.10H₂O; NaOH.H₂O; Na₃PO₄.12H₂O; LiCH₃COO.2H₂O; Al(NO₃)₂.9H₂O;Ba(OH)₂.8H₂O; Mg(NO₃)₂.6H₂O; KAl (SO₄)₂.12H₂O; MgCl₂.6H₂O;gallium-gallium antimony eutectic; gallium; cerrolow eutectic; Bi—Cd—Ineutectic; cerrobend eutectic; Bi—Pb—In eutectic; Bi—In eutectic;Bi—Pb-tin eutectic; Bi—Pb eutectic; CaCl₂.6H₂O and CaBr₂.6H₂O;Triethylolethane and water and urea; C₁₄H₂₈O₂ and C₁₀H₂₀O₂; CaCl₂ andMgCl₂.6H₂O; CH₃CONH₂ and NH₂CONH₂; Triethylolethane and urea;Ca(NO₃).4H₂O and Mg(NO₃)₃.6H₂O; CH₃COONa.3H₂O and NH₂CONH₂; NH₂CONH₂ andNH₄NO₃; Mg(NO₃)₃.6H₂O and NH₄NO₃; Mg(NO₃)₃.6H₂O and MgCl₂.6H₂O;Mg(NO₃)₃.6H₂O and MgCl₂.6H₂O; Mg(NO₃)₃.6H₂O and Al(NO₃)₂.9H₂O; CH₃CONH₂and C₁₇H₃₅COOH; Mg(NO₃)₂.6H₂O and MgBr₂.6H₂O; Napthalene and benzoicacid; NH₂CONH₂ and NH₄Br; LiNO₃ and NH₄NO₃ and NaNO₃; LiNO₃ and NH₄NO₃and KNO₃; LiNO₃ and NH₄NO₃ and NH₄Cl; or combinations thereof.

In some examples, the melting temperature of the PCM can be at leastabout −100° C. (e.g., at least about −50° C., at least about 0° C., atleast about 50° C., at least about 100° C., at least about 150° C., atleast about 200° C., at least about 250° C., at least about 300° C., atleast about 350° C. or at least about 400° C.). In some embodiments, themelting temperature of the PCM can be about 400° C. or less (e.g., about350° C. or less, about 300° C. or less, about 250° C. or less, about200° C. or less, about 150° C. or less, about 100° C. or less, about 50°C. or less, about 0° C. or less, or about −50° C. or less). The meltingtemperature of the PCM can range from any of the minimum temperaturesdescribed above to any of the maximum temperatures described above. Forexample, the melting temperature of the PCM can range from about −100°C. to about 400° C. (e.g., from about 0° C. to about 300° C., or fromabout 100° C. to about 200° C.)

In certain embodiments, the PCM comprises a salt water solution, and hasa melting temperature of from about −100° C. to about 0° C. In someembodiments, the PCM comprises a paraffin, and has a melting temperatureof from about 0° C. to about 150° C. In some embodiments, the phasechange material is a salt hydrate with a melting temperature of 50° C.to 100° C. In some embodiments, the phase change material comprises asugar alcohol, and has a melting temperature of from about 50° C. toabout 225° C. In some embodiments, the phase change material comprises anitrate, and has a melting temperature of from about 150° C. to about300° C. In some embodiments, the phase change material comprises ahydroxide, and has a melting temperature of from about 200° C. to about400° C.

In some embodiments, the melting enthalpy of the PCM can be at leastabout 100 MJ/m³ (e.g., at least about 150 MJ/m³, at least about 200MJ/m³, at least about 250 MJ/m³, at least about 300 MJ/m³, at leastabout 350 MJ/m³, at least about 400 MJ/m³, at least about 450 MJ/m³, atleast about 500 MJ/m³, at least about 550 MJ/m³, at least about 600MJ/m³, or at least about 650 MJ/m³). In some embodiments, the meltingenthalpy of the PCM can be about 100 MJ/m³ or less (e.g., about 650MJ/m³ or less, about 600 MJ/m³ or less, about 550 MJ/m³ or less, about500 MJ/m³ or less, about 450 MJ/m³ or less, about 400 MJ/m³ or less,about 350 MJ/m³ or less, about 300 MJ/m³ or less, about 250 MJ/m³ orless, about 200 MJ/m³ or less, or about 150 MJ/m³ or less). The meltingenthalpy of the PCM can range from any of the minimum values describedabove to any of the maximum values described above. For example, themelting enthalpy of the PCM can range from about 100 MJ/m³ to about 100MJ/m³ (e.g., from about 200-400 MJ/m³).

In some embodiments, the phase change material comprises a salt watersolution, and has a melting enthalpy of from about 150 MJ/m³ to about300 MJ/m³. In some embodiments, the phase change material comprises aparaffin, and has a melting enthalpy of from about 150 MJ/m³ to about200 MJ/m³. In some embodiments, the phase change material comprises asalt hydrate, and has a melting enthalpy of from about 200 MJ/m³ toabout 600 MJ/m³. In some embodiments, the phase change materialcomprises a sugar alcohol, and has a melting enthalpy of from about 200MJ/m³ to about 400 MJ/m³. In some embodiments, the phase change materialcomprises a nitrate, and has a melting enthalpy of from about 200 MJ/m³to about 600 MJ/m³. In some embodiments, the phase change materialcomprises a hydroxide, and has a melting enthalpy of from about 450MJ/m³ to about 700 MJ/m³.

As a result the CenoPCMs have several beneficial properties that makethem useful for building materials. For examples, the disclosed CenoPCMscan have high stiffness/strength. The cenosphere shell of a CenoPCM hasmuch higher stiffness/strength than a polymeric shell used in existingmicroencapsulated PCMs. As a result, CenoPCM can endure strong mixingduring the manufacturing of the materials, and will not significantlyreduce stiffness/strength of the produced materials.

The disclosed CenoPCMs can also have high chemical and thermalstability. Since cenospheres are hollow fly ash particles, they have thesame chemical and thermal stability as fly ash. When used in concrete,they can react slowly with the hydration product of Portland cement.This reaction will generate calcium silicate hydrate gel (CSH gel),which can make the CenoPCM shell even stronger.

The disclosed CenoPCMs can also have low flammability. Cenospheres arenonflammable and therefore can reduce the flammability of the PCM core,so that the disclosed CenoPCMs can be accepted by US building industry.

The disclosed CenoPCMs can also have high thermal conductivity. Sincecenospheres are inorganic, their thermal conductivity is much higherthan the organic polymeric shells used in existing microencapsulatedPCMs, making thermal exchange between PCMs inside the shell and outsideenvironment much easier and faster.

With all these advantages, CenoPCM can eliminate major barrierspreventing application of PCMs in traditional building materials. Forexample, CenoPCM can be integrated into construction and buildingmaterials to improve energy efficiency of buildings.

Also, disclosed are various building materials that comprise thedisclosed CenoPCMs. For example, disclosed herein is a compositioncomprising cement and the disclosed CenoPCMs. Also, disclosed herein isa composition comprising an insulating material and the disclosedCenoPCMs. Still further, disclosed herein is a composition comprising aroofing material and the disclosed CenoPCMs. In a further example,disclosed herein is a flooring material (e.g., tile, porcelain,linoleum, engineered hardwood) that comprises the disclosed CenoPCMs. Instill a further example, disclosed herein is a wall material (e.g.,gypsum, drywall, plaster, stucco, PVC) that comprises the disclosedCenoPCMs.

Other Admixtures

In another aspect, the disclosed compositions comprise an admixture asthe core material that is inside a cenosphere. One type of admixturethat can be included is an antimicrobial agent. Any antimicrobial agentthat can prevent or reduce microbial growth in the disclosedcompositions can be used. Examples of suitable antimicrobial materialsinclude metals such as copper, zinc, or silver and/or salts thereof.Further examples of suitable antimicrobial agents include natural andsynthetic organic compositions such as β-lactam antibiotics likepenicillin or cephalosporin, and protein synthesis inhibitors likeneomycin. Antimicrobial agents such as lactic acid, acetic acid, orcitric acid can also be used. In some other examples, an antimicrobialagent can comprise a quarternary ammonium compound such as benzalkoniumchloride, benzethonium chloride, methylbenzethonium chloride,cetylalkonium chloride, cetylpyridinium chloride, cetrimonium,cetrimide, dofanium chloride, tetraethylammonium bromide,didecyldimethylammonium chloride, and domiphen bromide. Theantimicrobials can be used in effective amounts, e.g., an amount thatwill prevent or reduce microbial growth. Thus disclosed herein arecompositions comprising a cenosphere and an antimicrobial agent, whereinthe antimicrobial agent is encapsulated inside the cenosphere.

Another suitable admixture that can be used in the disclosedcompositions is a fire retardant. Suitable fire retardants can comprisean organic composition or an inorganic composition. In some examples, asuitable fire retardant such astris(2-chloro-1-(chloromethyl)ethyl)phosphate, aluminum hydroxide,magnesium hydroxide. In some embodiments, a fire retardant can comprisea zeolite. The fire retardants can be used in effective amounts, e.g.,an amount that will prevent or reduce combustion. Thus disclosed hereinare compositions comprising a cenosphere and a fire retardant, whereinthe fire retardant is encapsulated inside the cenosphere.

Still further, another suitable admixture that can be used in thedisclosed compositions is a corrosion inhibitor such as sodium sulfite,chromates, and polyphosphates. Thus disclosed herein are compositionscomprising a cenosphere and a corrosion inhibitor, wherein the corrosioninhibitor is encapsulated inside the cenosphere.

In yet another example, the disclosed compositions can comprise water asan admixture. This composition can be used to promote self curingproperties into concrete. Thus disclosed herein are compositionscomprising a cenosphere and water, wherein the water is encapsulatedinside the cenosphere.

In still another example, the disclosed compositions can comprise awater reducer as an admixture. Thus disclosed herein are compositionscomprising a cenosphere and a water reducer, wherein the water reduceris encapsulated inside the cenosphere. Examples of water reducers arelignosulphonates, hydroxycarboxylic acids, carbohydrates, and otherspecific organic compounds, for example glycerol, polyvinyl alcohol,sodium alumino-methyl-siliconate, sulfanilic acid and casein asdescribed in the Concrete Admixtures Handbook, Properties Science andTechnology, V. S. Ramachandran, Noyes Publications, 1984.

In yet another example, the disclosed compositions can comprise aviscosity modifier as an admixture. Cellulose, PEG—Glycol derivative,Natural Gums, amorphous silica, and the like. Thus disclosed herein arecompositions comprising a cenosphere and a viscosity modifier, whereinthe viscosity modifier is encapsulated inside the cenosphere.

In yet another example, the admixture can be a superplasticizer, such asa polyacrylate aqueous solution. Thus disclosed herein are compositionscomprising a cenosphere and a superplasticizer, wherein thesuperplasticizer is encapsulated inside the cenosphere.

In yet another example, the admixture can be air. Thus disclosed hereinare compositions comprising an empty perforated cenosphere, wherein airis encapsulated inside the cenosphere.

Other examples of admixtures that can be incorporated into cenospheresare listed below.

Freeze and freeze-thaw resistance Sterically or electrostaticallyrepelling monomers Shrinkage and degradation Mineral oils or surfactantsresistance Low hydration heat release Heat retarding agents Low waterabsorption Polyurethane Noise absorption/insulation Organic solvent withmagnetic particles Reversible color changes Thermochromic materialsSelf-healing Healing agentsMethods

The disclosed compositions can be prepared by a method generallyillustrated in FIG. 1. While this method is illustrated with PCM as thecore material, other core materials or admixtures disclosed herein canbe used. In the first step, perforated cenospheres can be producedthrough acid etching. To introduce PCM into a cenosphere, theglass-crystalline nanosize film on the surface of the cenosphere must beremoved. This can be done through acid etching, e.g., using 1.0 MNH₄F-1.2 M HCl—H₂O for 2 hours. After removing the nanosize film,perforated cenospheres with very small holes (smaller than 2 μm)penetrating through the shell can be produced (FIG. 2C).

The acid solution can contain be a hydrofluoric acid based solution. Forexample, solutions of hydrofluoric acid and ammonium hydroxide (e.g.,comprising ammonium fluoride, HF, water) can be used. Other hydrofluoricacid solutions can be used as well, e.g., those comprising hydrofluoricacid and hydrochloric acid, to produce perforated cenospheres.

Next, liquid PCMs are loaded into the perforated cenospheres (FIGS. 3Aand 3B). In the following examples, paraffin waxes (n-alkanes) areloaded, though any PCM can be used. Paraffin waxes have phase-changetemperatures of 18-36° C. and can change phases within this temperaturerange, making humans feel comfortable. Therefore, they can be used tointegrate construction materials to regulate the temperature of thebuilding. Loading Paraffin wax into perforated cenospheres can be doneby mixing cenospheres in liquid wax to let liquid wax penetrate into thehollow cenospheres. Before loading with liquid wax, cenospheres canfloat on liquid wax as shown in FIG. 3A. After loading, cenospheressettle down at the bottom of the container as shown in FIG. 3B. Afterloading, the extra paraffin wax absorbed on the surface of thecenospheres can be washed by distilled water before it changes its phaseto solid, or can be washed using organic solvent such as acetone afterit is solidified.

A thin layer of silica can be coated on the PCM loaded cenospheres toprevent the possible leaking of the liquid PCM, as shown in FIG. 4. Thiscoating can be applied by spray-drying method as shown in FIG. 4. Forexample, PCM loaded cenospheres can be mixed with commercially availablesilica sol and then sprayed into the drying chamber, in which the silicasol is heated to form a very thin layer of silica. This layer of silicacan not only seal the perforated holes on the cenosphere shells, butalso strengthen the cenosphere shells. This process can be performedwith other materials as well, such as alumina or titania.

The sol-gel method can also be used to prepare the silica nanoparticlesolution. Tetraethoxysilane (TEOS) can be used as the precursor forsol-gel synthesis since it reacts readily with water with either a basicor acidic catalyst. This reaction is called hydrolysis, because ahydroxyl ion becomes attached to the silicon atom. The process comprisesa series of hydrolysis and condensation reactions of the TEOS, as shownin FIG. 8. Sol-gel reactions do not require extreme reaction conditions.The reactions can take place at room temperature and require onlymoderate temperatures to ‘cure’ the gel, which can easily remove theexcess materials generated by the reaction. In this method, silica solcan be prepared through hydrolysis of TEOS with ammonium hydroxide or anitric acid solution as catalyst. Then a dip coating method can be usedto apply the silica sol on the surface of cenospheres to form a porousthin film of nanosilica.

Alternatively, a thin layer of TiO₂ can also be coated on censpheres toadd a self-cleaning function to the concrete. This thin layer ofnanoparticle coating can be applied before or after the loading of theadmixture, depending on the nature of the intended application.

In addition, a thin layer of polymer can also be coated on thecenosphere to seal the perforated cenosphere shell. Any polymer whichsufficiently adheres to the cenosphere shell can be used for coating.

The disclosed methods can also comprise the step of adding the disclosedcompositions into a building material, such as concrete, mortar, cement,asphalt, tar, tile, brick, ceramics, gypsum, plaster, stucco, porcelain,linoleum, engineered hardwoods, PVC, insulation, roofing and flooringmaterials, and the like. A recent Oak Ridge National Laboratory (ORNL)study indicated that PCM integrated wallboard can result in up to 22%electricity savings from wall-generated cooling loads (Biswas et al.,2014. Applied Energy, 131,517-529). Another study showed both coolingand heating energy savings are achievable with distributed PCM mixedwith cellulose insulation in wall cavities (Biswas et al., 2014 EnergyConversion and Management, 88, 1020-1031).

In one specific example, the disclosed methods comprise adding thedisclosed compositions to concrete. Portland cement-based concrete (PCC)is the most widely used construction material in our civilinfrastructure system, accounting for 70% of all building andconstruction materials. Manufacturing of PCC not only consumes largeamounts of natural resources, but also produces considerable greenhousegases. Cement production in the U.S. accounts for up to 7% of thenation's total CO₂ emissions. PCC is also susceptible to deteriorationwhen exposed to harsh environments. Low tensile strength, highbrittleness, and low volume stability make PCC vulnerable to cracking.PCC's higher permeability, porous microstructure, and thermodynamicallyunstable chemical compounds such as calcium silicate hydrate (CSH) makeit susceptible to acid and sulfate attack. Deterioration of PCC hasemerged as one of the largest challenges in maintaining and protectingthe U.S. civil infrastructure system.

To this end, the disclosed compositions can be a versatile low cost toolfor concrete manufacturing that minimizes or avoids undesiredinteractions between the admixtures and hydration of cement through thecontrolled release of admixture or through sealing the admixtures inconcrete. The disclosed compositions can load and then release or sealthe admixtures within concrete as needed. As a result, optimal effectsof the admixture can be reached and/or new desirable functions can beadded to concrete.

EXAMPLES

The following examples are set forth below to illustrate the methods andresults according to the disclosed subject matter. These examples arenot intended to be inclusive of all aspects of the subject matterdisclosed herein, but rather to illustrate representative methods andresults. These examples are not intended to exclude equivalents andvariations of the present invention which are apparent to one skilled inthe art.

Efforts have been made to ensure accuracy with respect to numbers (e.g.,amounts, temperature, pH, etc.) but some errors and deviations should beaccounted for. Unless indicated otherwise, parts are parts by weight,temperature is in ° C. or is at ambient temperature, and pressure is ator near atmospheric. There are numerous variations and combinations ofconditions, e.g., component concentrations, temperatures, pressures, andother reaction ranges and conditions that can be used to optimize theproduct purity and yield obtained from the described process. Onlyreasonable and routine experimentation will be required to optimize suchprocess conditions.

Example 1

A commercially obtained cenosphere (FIGS. 2A and 2B) was etched withacid to remove the glass-crystalline nanosize film on the surface.Before each acid treatment, cenospheres that were formed with naturalperforations during the combustion process were removed from the bulkmaterial via water filling under vacuum followed by gravity separation.Only the cenospheres with complete shell were selected for etching,shown as in FIG. 2A. After etching in 1.0 M NH4F-1.2 M HCl—H2O solutionfor 2 hours, the cenospheres were vacuum filtered and rinsed with waterto remove the residual acid. The collected and washed spheres were thensoaked in water to separate the ones floating on the surface from theones sinking to the bottom. The sinking ones were perforated cenospheresand they were collected and then dried in oven at 100° C. for 24 hours.The etching resulted in a perforated cenosphere (FIG. 2C). Theperforated cenosphere was then added to water as the core material. Theloaded cenosphere precipitated to the bottom of the vessel. It wasdetermined that the water absorption of the perforated cenosphere couldreach as high as 180%, which is much higher than that of light weightaggregates typically used. This percentage ratio is the weight of waterabsorbed by the cenosphere to the weight of the cenosphere. For example,in this example, one pound perforated cenospheres can absorb 1.8 poundof water.

Example 2

The same procedure as Example 1 was followed except that paraffin waxeswere used as the core material.

FIG. 6A, shows Differential Scanning calorimetry (DSC) testing resultson the CenoPCM. The following procedure was used to perform the DSCmeasurement: heating/cooling rate=5° C./min, temperature program-scanstarted at 10° C. and was complete at 50° C. A continuous ascending anddescending scan was utilized during dynamic DSC testing. Panel (a)indicates that the peak melting and freezing temperatures and the latentheats of the CenoPCM are 23.83° C., 21.57° C., 119.83 J/g, 128.04 J/g,respectively. Table 1 compares latent heats of the CenoPCM with twocommercially available microencapsulated PCMs (Zhang, et al., Thermaland rheological properties of microencapsulated phase change materials.Renewable Energy 2011; 36:2959-2966). Table 1 shows that compared withthese commercially available microencapsulated PCMs, CenoPCM is superiorin latent heat storage capacity.

TABLE 1 Comparison of latent heat of CenoPCMs with commerciallyavailable MEPCMs Microcapsule name Melting latent heat (J/g) Freezinglatent heat (J/g) 1 102.01 106.4 2 96.97 101.01 CenoPCM 119.83 128.04

FIG. 6B shows thermogravimetry analysis (TGA) results of unsealedCenoPCM. It can be seen that the CenoPCM starts to lose weight at 150°C. because PCM decomposes at this temperature. Since the cenosphereswere not sealed, decomposed PCM vapor was quickly lost from theperforated cenospheres. This process continued until temperature reached220° C. After this temperature, no further weight loss can be observedfor the CenoPCM sample, suggesting that all PCM inside the perforatedcenospheres had been evaporated. The residual weight of the sample isthe weight of the perforated cenosphere shell. From the TGA measurementshown in FIG. 6B, it was found that: 1) the PCM accounts for 63.64%total weight of the produced CenoPCM, suggesting that cenosphere hasvery high absorption of PCMs; and 2) no decomposition occurred in thecenosphere shell within the testing temperature ranges (800° C.),suggesting that cenospheres have much higher thermal stability thanpolymer shells used in existing microencapsulated PCMs.

Example 3

The compositions produced in Example 2 were combined into concrete.These cenospheres were compared with commercially availablemicroencapsulated PCMs. FIG. 5A, shows that a commercially availablemicroencapsulated PCM appears to a large extent deformed and broken,suggesting that a large portion of that product cannot survive duringthe mixing process of concrete (Hunger M, et al. The behavior ofself-compacting concrete containing micro-encapsulated Phase ChangeMaterials. Cem Concr Compos 2009; 31:731-43). Similarly, a large portionof another commercially available microencapsulated PCM can also beidentified from FIG. 5B (Dehdezia P K, et al. Thermal, mechanical andmicrostructural analysis of concrete containing microencapsulated phasechange materials. International Journal of Pavement Engineering 2013;14:449-462).

FIG. 5C shows a broken cenoPCM particle. It can be seen clearly that PCMcan be successfully loaded into the cenosphere shell.

FIG. 5D is the SEM image of the concrete added with 5% CenoPCMmicrocapsules. It can be seen that most of these particles are intact,verifying that the proposed CenoPCM has much higher strength thanexisting polymer based microencapsulated PCMs.

Table 2 shows the effect of adding 5% CenoPCM on the strength ofconcrete. It can be seen that 15% of strength reduction can be inducedby CenoPCM. This is mainly caused by the PCM absorbed on the surface ofthe CenoPCM, which absorbs some mixing water in concrete and thereforereduces the workability of concrete. If we wash the CenoPCM better, thisstrength reduction will become insignificant. As comparison, afteradding 0.5 wt %, 1 wt %, 3 wt % and 5 wt % CIBA's phase change materialsmicrocapsules, the percentage reduction in strength is approximately25%, 45%, 70% and 80% for addition, respectively.

TABLE 2 Strength reduction induced by CenoPCM addition Age 3 days 7 days28 days Without CenoPCM (psi) 4666 5340 7368 With CenoPCM (psi) 39144837 6219 Reduced (%) 16 13 15

Example 4

A mesoporous thin film can be coated on the surface of the loaded,perforated cenosphere. This can reduce the permeability of thecenosphere wall for applications requiring very slow release or sealingof the admixture, and enhance the mechanical performance of concrete.The thin film can be silica, alumina, or titania, which can provide aself-cleaning function to the concrete. This thin layer coating can beapplied before or after the loading of the admixture, depending on thenature of the intended application.

The sol-gel method can be used to prepare a silica nanoparticle solutionbecause of its low cost and ease of implementation. Tetraethoxysilane(TEOS) can be the precursor for sol-gel synthesis since it reactsreadily with water with either a basic or acidic catalyst. The processcomprise a series of hydrolysis and condensation reactions of the TEOS(FIG. 8). Sol-gel reactions do not require extreme reaction conditions.The reactions can take place at room temperature and require onlymoderate temperatures to cure the gel, which can easily remove theexcess materials generated by the reaction.

In a specific method, silica sol can be first prepared throughhydrolysis of TEOS with ammonium hydroxide or a nitric acid solution ascatalyst. Then a simple dip coating method can be used to apply thesilica sol on the surface of cenospheres to form a porous thin film ofnanosilica. The permeability of this thin film can be determined by thepacking properties of the nanosilica, which can be controlled by theconcentration of the precursor and the pH value of the sol. In otherwords, the loading/releasing properties of the nanosilica coatedcenosphere can be further modified by adjusting the concentration ofTEOS and pH value of the sol.

Nanosilica particles can not only have pozzolanic reaction with calciumhydroxide, but also can serve as nucleating sites for the hydrationreaction of cement to promote the production of CSH. As a result, a verydense interface transition zone between the cenosphere and cement pastecan be produced. This dense interface can significantly increase thestrength of the concrete. In addition, the produce dense interfacetransition zone can provide extra measure to prevent leaking of someadmixture (e.g., PCM).

Coating the cenospheres with nanosilica thin films can also eliminate adrawback of traditional addition of nanoparticles as a dry powderadditive to concrete—poor dispersion of the nanoparticle. Due to strongvan der Waals forces between nanoparticles, nanoparticles tend toconglomerate. To achieve good dispersion of nanoparticles in concrete,strong physical blending using ultrasonic waves or chemicalfunctionalization are commonly used. With the disclosed compositions,silica nanoparticles are directly grown on the surface of cenospheres.After homogeneously mixing these cenospheres into cement mixture, thesilica nanoparticles are self-dispersed into the cement matrix. In thisway, the time-consuming and difficult task of dispersing nanoparticlesis eliminated.

Also, there is less risk of silica inhalation when the silicananoparticles are coated on the cenosphere.

FIG. 9A shows a CenoPCM coated with a thin layer of nanosilica through asol-gel method.

Organic polymers can be coated on the perforated cenospheres thoughspray drying, fluidized bed, or other known techniques. FIG. 9B showssome perforated cenospheres with a polymer coating.

Example 5

Internal curing is a relatively new manufacturing method for highperformance concrete. In this method, saturated LWAs or SAPs aretypically used as water reservoirs to continuously supply water toreplenish the empty pore volume that is created by self-desiccation.This will reduce autogenous shrinkage and also improve the curing ofconcrete at the early age. Thus, internal curing can be used to producea dense crack-free microstructure, which is the desire of using a lowwater-to-cement ratio (w/c). Benefits of internal curing have also beenshown to include reduced shrinkage of sealed concrete, increasedcompressive strength and flexural strength (especially at later ages),reduced potential for cracking and increased durability.

When used in internal curing for concrete, water loaded withincenospheres has to be readily available to be released to thesurrounding cementitious matrix in order to optimize internal curing ofconcrete. An ideal internal curing agent should release most of itsabsorbed water at high relative humidity within an appropriate time. Inthis example, the water release from the cenospheres at two differentrelative humidity levels: 50% and 95%, was performed. The results areshown in FIG. 10. It can be seen that even under high relative humidity(95%), more than 90% of loaded water can be released within 24 hours,suggesting that perforated cenospheres are an excellent internal curingagent. Direct observation of water movement during the first three daysof the curing of a w/c=0.3 mortar specimen containing pre-wetted fineLWA shows that much of the water within the pre-wetted LWA departedduring the first day of (rapid) hydration of the cementitious matrix.These data indicate that the release rate of water agrees with thisrate. So water can not only be introduced into cenospheres, it can beproperly released into cement matrix when needed. FIGS. 11A through 11Cshow SEM images of the microstructure of a concrete with water to cementratio of 0.34 with and without cenospheres as internal curing agent.FIG. 11A is a concrete without internal curing with significant amountof drying shrinkage cracks. FIG. 11B is a concrete with cenospheres asinternal curing agent showing cenospheres are evenly dispersed inconcrete and much less drying shrinkage cracks. FIG. 11C is a brokencenosphere in concrete showing water is released and very densehydration products around it. In addition, perforated cenospheres enjoyat least three additional advantages over existing internal curingagents such as LWAs or SAPs: 1) They have very high absorption (120% oreven higher) which is much higher than lightweight aggregates (5˜40%). Amuch smaller amount of cenospheres is needed to provide internal curingwater; 2) They are very small in size. Therefore, a more spatiallyuniform distribution of internal curing water can be provided bycenospheres; 3) Cenospheres have pozzolanic reactivity, which will reactwith calcium hydroxide (CH) produced from cement hydration at late age.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope or spirit of the invention. Otherembodiments of the invention will be apparent to those skilled in theart from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A method of encapsulating a core material insidea cenosphere, the method comprising: contacting a cenosphere with anacid solution, thereby providing a perforated cenosphere; contacting theperforated cenosphere with the core material, thereby encapsulating thecore material in the perforated cenosphere; and coating the perforatedcenosphere encapsulating the core material with silica, alumina, or apolymer, wherein the coating is by spray drying; wherein the corematerial comprises a phase change material, and wherein the phase changematerial comprises a salt-water solution, a sugar alcohol, a paraffin, afatty acid, a salt hydrate, a nitrate, a hydroxide, a hygroscopicmaterial, or combinations thereof.
 2. The method of claim 1, wherein theperforated cenosphere has an average diameter of from about 1 μm toabout 2,000 μm.
 3. The method of claim 1, wherein the phase changematerial comprises a fatty acid, a salt hydrate, or combinationsthereof.
 4. The method of claim 1, wherein the phase change material isparaffin wax.
 5. The method of claim 1, wherein the core materialfurther comprises water.
 6. The method of claim 1, wherein the phasechange material has a melting temperature of from −100° C. to about 400°C.
 7. The method of claim 1, wherein the phase change material has amelting enthalpy of from about 150 MJ/m³ to about 300 MJ/m³.
 8. Themethod of claim 1, wherein the core material further comprises aconcrete admixture.
 9. The method of claim 1, wherein core materialfurther comprises an antimicrobial agent, a fire retardant, a corrosioninhibitor, a viscosity modifier, superplasticizer, or air.
 10. Themethod of claim 1, wherein the acid solution comprises ammonium fluorideand hydrochloric acid.